L03J602 铝合金门窗 山东省建筑图集.pdf

Oracle8i SQL&PLSQL基础
Oracle8i SQL_02
Database Transactions
Consist of one of the following statements:
DML statements that make up one consistent change to the data
One DDL statement
One DCL statement
Database Transactions
Begin when the first executable SQL statement is executed
End with one of the following events:
COMMIT or ROLLBACK
DDL or DCL statement executes (mit)
User exits
System crashes
Advantages MIT and ROLLBACK
Ensure data consistency
Preview data changes before making changes permanent
Group logically related operations
DELETE
Controlling Transactions
Transaction
Savepoint A
ROLLBACK to Savepoint B
DELETE
Savepoint B
COMMIT
INSERT
UPDATE
ROLLBACK to Savepoint A
INSERT
UPDATE
INSERT
ROLLBACK
INSERT
An mit occurs under the following circumstances:
A DDL statement is issued
A DCL statement is issued
A normal exit from SQL*Plus, without explicitly MIT or ROLLBACK
An automatic rollback occurs under an abnormal termination of SQL*Plus or a system failure
Implicit Transaction Processing
State of the Data Before COMMIT or ROLLBACK
The previous state of the data can be recovered.
The current user can review the results of the DML operations by using the SELECT statement.
Other users cannot view the results of the DML statements by the current user.
The affected rows are locked; other users cannot change the data within the affected rows.
State of the Data MIT
Data changes are made permanent in the database.
The previous state of the data is permanently lost.
All users can view the results.
Locks on the affected rows are released; those rows are available for other users to manipulate.
All savepoints are erased.
Committing Data
SQL> UPDATE emp
2 SET deptno = 10
3 WHERE empno = 7782;
1 row updated.
Make the changes.
Commit the changes.
SQL> COMMIT;
plete.
State of the Data After ROLLBACK
Discard all pending changes by using the ROLLBACK statement.
Data changes are undone.
Previous state of the data is restored.
Locks on the